Plant tissue culture methods have been used for more than 30 years to clone and propagate a large variety of plants. The conventional method, using semisolid (agar) medium, has been widely used due to its simplicity and low costs. However, the huge amount of labour is a major disadvantage. New technologies have been developed to reduce the handling time, while increasing the multiplication rates and plant quality. As a result, the Temporary Immersion System (TIS), also called Temporary Immersion Bioreactor (TIB), was created in the 80’s.

The principle of TIS technology is that plant material is immersed in growth media for short periods, and at regular intervals. These immersions are sufficient for the plants to take up the nutrients. TIS technology makes use of the advantages of liquid cultures, while growing the plant material under high gas-exchange environments.

TIS bioreactors are divided in two main groups: 1) Commercially available bioreactors, and 2) ‘self-built’ bioreactors.

Production of more plants per square meter

Higher multiplication rates

Use of liquid medium reduces agar costs

Higher nutrient uptake

Reduced manipulations and labour

Forced aeration increases growth and biomass production

Improved plant quality

Semi‐automated

Examples of self-built TIS bioreactors

The use of self-built TIS bioreactors in large-scale plant propagation is quite complex, mostly because they use system elements which are not designed for in vitro plant propagation. Hence, some of the common disadvantages of these systems are: suboptimal use of growth chambers and light sources, reduced material homogeneity and plant quality, high contamination risks, limitations to develop protocols for different plant species, short system lifetime, and complex assembly and sterilization processes.

Comparing agar to TIS

Advantages of TIS technology

Available TIS are used for research, not for commercial propagation

Self-built TIS bioreactors also have limitations

The system is driven by compressed air generated in the air compressor. The air entrance is controlled by two valves (1 & 2). During the Stationary phase, both valves are closed. No transfer of media takes place, allowing plant material to grow.

During the Immersion phase, valve 2 is opened, rising the air pressure in the media vessel so that the growth media is transferred to the culture vessel. During this phase, plant material is immersed in growth media, allowing nutrient uptake.

Once the Immersion phase is finished, valve 2 is closed and valve 1 is opened. Using the same principle but in opposite direction, the growth media is completely returned to the media vessel.

Few commercial TIS bioreactors have been brought into the market, but none has been successfully introduced in commercial plant micropropagation labs. Major limitations, such as their inadequate culture volume, and their complexity in assembly and lab setup, have reduced its use exclusively for research purposes.

As a consequence, commercial micropropagation labs are currently using their own ‘self-built’ TIS bioreactors, made up from alternative parts from local markets. Based on the simplicity and excellent concept of the Twin-bottles principle, these self-built bioreactors separate plant material and growth media in two connected vessels.

Principle of TIS technology using Twin-bottles

To overcome all these problems, was then SETIS™ generated. The ultimate TIS bioreactor for plant micropropagation.